Insulating material



March 4, 1930. H, G, WALKER 1,749,008

INSULATING MATERIAL Filed Aug. 3l, 1927 L 1' f v I Patented Mar. 4, 1930 UNITED STATES PATENT OFFICE 'HOWARD GEORGE WALKER, OF LA GRANGE, ILLINOIS, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK INSULATING MATERIAL Application mea August 31, 1927. serial 110.216,625.

This invention relates generally to insulating materials, and more particularly to water l resistant, insulating materials.

Many insulating materials have sufficient water repellarit properties to permit their use when they are subjected only to'atmospheric v moisture, or to more severe conditions for short periods of time, but due to their water absorbent properties most of them are unsuited for use Where they are continuously exposed to extremely humid conditions or' are submerged in' Water.

The present invention has for its object the provision of an insulating material having desirable insulating characteristics and also having the property of retarding the passage of moisture therein so that the effective life of the insulating material. in the presence of moisture is materially lengthened.

In accordance with the general features of the invention, an insulating material of any suitable type, such as'a rubber compound, is prepared and finely divided particles of a j non-corrosive material having a large surface area capable of retaining moisture are dispersed throughout the rubber compound.

The resulting composition may then be applied to the article to be insulated, such as an electrical conductor, and vulcanized thereon.

It is believed that the invention will be clearly understood from the following detailed description of specific embodiments of the invention taken in conjunction with the accompanying drawing, in which Fig. 1 is a fragmentary longitudinal view of a portion of acable embodying the invention; f

Fig. 2 is a transverse sectional view thereof taken on line 2-2Cof Fig. 1;

Fig. 3 is a fragmentary longitudinal view of another type of cable embodying the invention, and

v Fig. 4 is a transverse sectional view thereof l taken on line 5 4 of Fig. 3.

Numerous experiments have shown that practically all electrical insulating materials absorb water'to a greater ora lesser degree and, in view of this fact, insulating compositions of the type which form the subject matter of this invention have been developed to lportion of an electric cable in which the insulating material has been utilized to protect the conductor therein from moisture. Referring n ow to those figures, the numeral 10 designates an electrical conductor around which a plurality of conductors 11-11 are arranged in the form of helices. Surrounding the conductors 10-and 11-11 is a layer of insulating material 12 comprising a rubber com ound 13 throughout 'which are dispersed particles 14-14 of a non-corrosive material, such as silica gel, having a large surface area capable of retaining moisture. This layer of insulating material is in turn surrounded by another layer 15 of a suitable insulating and waterproof material, such as a rubber cornpound, which is substantially impervious to water and the layer 15 is covered by a strip of fabric 16 wound spirally therearound, which may in turn be covered with additional protective layers if desired.

A suitable composition for use in the layer 12 is as follows:

Smoked sheet rubber to 55% Hard rubber dust 18 to 28% Silica gel 15 to 5%' Zinc oxide 7.75% Litharge 6.25% Sulphur 2% Paratlin 1% lThis composition may be applied to the conductors by extrusion or by any of the other usual methods and vulcanized thereon in any 'conductors 10 and 11-11. However, instead 'of the moisture penetrating the layer of insulating material 12 and coming directly into `contact with thek conductors 11-11 and 10,

' tinue to absorb and retain any moisture which penetrates through the insulating layer 15 and thereby prevent the moisture from reaching the conductors-surrounded 'by the insulatingA layer 12 until the particles 14w14 have become substantially saturated With Water. It Will thus be seen that although the insulating material forming the subject matter of this invention does not completely inhibit the passage of moisture therethrough, it materially lengthens the period of time required for moisture to penetrate from the outside of the layer of materialtothe inner portions thereof.

Another type of cable employing the insulating material is disclosed in Figs. 3 and 4:, in which the numerals 20 and 21 indicate a pair of electrical conductors Which are `surrounded and separatedby an insulating material 22 of the same type as the insulating material forming the layer 12 in the cable illustrated by Figs. 1 and 2, and the insulating material 22 is in turn enclosed Within a lead Figs. 2 and 3 is especially useful for power lar insulating and protective properties, and the term insulating material as used hereinbefore and in the annexed claims is intended to include all of the above mentioned materials.

What is claimed is:

1. An insulating material comprising approximately 50 to 55% rubber, 18 to 23% hard rubber dust, 15 to 5% silica gel, 7.75% zinc oxide, 6.25% litharge, 2% sulphur, and 1% paraiiin.

2. An insulating material comprising approximately 50 to 55% rubber, 25.75 to 30.75% fillers, 15 to 5% silica gel, 8.25% Vulcanizing ingredients, and 1% paratlin.

In Witness whereof, I hereunto subscribe my name this 17th day of August A. D., 1927.

HOWARD GEORGE WALKER.

purposes in mines, etc., where it would be sub- ]ected to extreme conditions of moisture. Although the lead sheath 23 will under ordinary circumstances exclude moisture from the in' terior of the cable, if the .sheath should be broken the Water absorbing particles dispersed throughout the layer 22 would absorb andaretain any moisture which enters the breachfor a considerable length of time and Wouldthereby delay the complete failure of the cable.

It is, of course, to be understood that the lnvention is not to be limited to the specific composition disclosed hereinbefore but is limited only by the spirit and scope of the annexed claims. For example, another composition Which is suitable for uses similar to those described above is as follows:

\ Smoked-sheet rubber 49% Powdered silica 30 to 35% Silica gel -10 to 5% Zinc oxide 3% Litharge 5% Sulphur 2% Parafn 1% 

